I know that typically spray foam is a bad thing to use around windows because of the expansion pressure bowing window and door frames however I see that spray foam manufacturers now offer low pressure foams specifically for windows and doors. I'm sure that most window manufacturers will strongly advise against it as will most installers however is this simply and old prejudice against the old style foams that is just dying hard? I'm having new windows installed soon and I'm torn about what to use. I'm convinced that spray foam is superior to fiberglass insulation in it's ability to insulate, seal and support a window however if you risk deforming the window it's obviously a bad choice. So what's the general opinion about foam insulation? Are the new formulas for windows safe to use?

Skydog, we use canned foam everyday. Years ago when the only foams were "High Expansion" foams that would push concrete blocks apart were your only choice. The industry put the clamps to not using it. It would void any warranty if they seen it used on any door or window product. Today the game is different. With the invention of "Low Expansion" faoms we are safe from the pressurized deforming of the high expansion product. The two we use are "Great Stuff" in the light blue can NOT THE RED CAN and "Dows" low expansion foam in the white can. Just make sure you get the "LOW EXPANSION" and you will be fine. Just be careful not to go gangbusters in the gaps. This stuff will be all over the place. Go slow and take your time. I can't stress the fact you be patient and not over do it. Do one window and get the feel for it before going on. Let the foam expand so you can see what it does before you go to the next opening. Good Luck!!!

The only downfall to the stuff is if service is needed such as readjusting shimming tightness or having to readjust the window frame to adjust the squareness, you are in a world of hurt because the stuff grabs hold and is a pain in the rear to work with. I used it for a while with really no problems, but I personally prefer fiberglass when installing in existing homes. I install the fiberglass BEFORE I square and screw in the new window to make sure it's insulated in the very small gaps that are created by out of square openings. You can't do that with foam. On new Construction installations where the gaps are larger I would use the foam pretty much 100% with no reservations.
On another note, some manufacturers still have it in their warranty that the use of foam will void the warranty. Just to be safe, I would check the warranty before letting an installer use foam.

I tend to lean in favor of the low-expanding foam. It has a much higher R-value than fiberglass and it provides an air-seal as well. Keep in mind that any type of insulation is only effective when combined with a pressure boundary (air seal). Without it, insulation is only an air filter. The good installers like Guy or Windows4U properly air seal in other ways but you may be less fortunate with many of the others. To my knowledge, the use of foam will only compromise the coverage of your warranty if compression from it is deemed to be the exclusive cause of the failure.

Well if you listen to these two guys above this you'll never get anything done right. Who would ever have to service a product if done right the first time!, I'm just kidding about them......they have some good points that I overlooked because of habit. What type of insulation we use depends on the job itself. Most of the low expansion foam stays soft so we can adjust if needed. Also small voids are much easier to fill with fiberglass. We will also use a Swedish made product called CC Sealer for tight spots and odd areas. It's quite expensive but really is the ultimate in insulation. It's a two inch wide tape that is pin nailed around the opening before the unit is installed. It's around 1/16" thick with a self stick activation paper to the outside. Ounce in place we reomove the activation paper and install the window. After the window is squared and leveled it is screwed in place. The tape then activates and expands after an hour or so. It expands up to 1-1/4"and stays pliable for ever. Even if the window moves it will re-activate and fill the gap. It's great stuff but adds about $20 to each window in cost. We do all new construction with foam as W4U does. They do point out a good fact that you should always check your manufacturers specs before using. There are a few companies who will void a warranty if you use foam. So make sure you can use it.

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